Various types of hand tools have been devised for performing various operations such as power actuated drills, nailers, grinders, stitchers, meat cutting and trimming tools, etc. which are operated by a power driven flexible drive shaft, or an air motor mounted within the hand tool and powered by pressurized air supplied to the motor by a fluid supply line. The flexible drive shafts are driven by an electric motor located remote from the hand tool. Of these various hand tools power driven meat cutting knives have been used extensively in the meat industry to facilitate the removal of meat from a carcass, primarily in a trimming operation, or for removing the meat remains from the bones. The present invention is described below with particular reference to such meat trimming knives, although the control system is adaptable for other power operated hand tools and need not be limited to such meat trimming knives.
Prior examples of electrically driven trimming knives using flexible drive shafts are shown in U.S. Pat. Nos. 3,269,010; 4,179,063; 4,178,683; 4,198,750; 4,494,311 and 4,575,938. In these electrically driven knives, the flexible drive shaft is connected at one end to the electric motor which is located adjacent to the work area and enters the rear of the handle portion of the knife and extends through the handle bore and terminates in a squared end. The squared end is engaged in a complementary-shaped opening formed in the rear of a pinion gear which rotatably drives the cutting blade mounted on the front of the handle. In pneumatically driven knives, such as shown in U.S. Pat. No. 3,852,882, the output shaft of the air motor is engaged through a gear assembly with the rear opening of the pinion gear for driving the gear and correspondingly driving the cutting blade in a similar manner as does the pinion gear of the electric knives.
These power driven tools, or trimming knives as they are generally referred to in the industry, whether electrically or pneumatically driven, consist of a tubular handle terminating in a generally arcuate-shaped front end and have a hollow bore extending throughout the longitudinal length of the handle. An annular blade holder is attached to the arcuate front end of the handpiece and has a ring blade removably mounted thereon by various mounting arrangements. The blade is formed with gear teeth extending around the top edge which are in driving engagement with the pinion gear rotatably mounted within the front end of the handpiece adjacent the ring blade.
These meat trimming knives, whether pneumatically or electrically driven, are used for relatively long periods of time by an operator at a work station in a relatively cold environment, which is required to maintain the meat being trimmed in a safe condition. The operator usually is positioned at a work station and the meat is continuously brought to the work station on a conveyor, or the like, for trimming the meat from the carcass or bones by the operator.
An operator will start and stop the rotation of the cutting blade of the electrically driven knife by actuating the main switch on the electric drive motor mounted overhead of the work station. This necessitates the operator reaching overhead each time he or she wishes to start and stop the electric drive motor and, consequently, the cutting blade. Due to the amount of motion that must be performed by the operator to start and stop the trimming knife, the operator usually will permit the main electric motor and knife blade to continue to run between brief pauses in the trimming of meat from different carcasses as they are brought to the operator. This requires the operator to continually maintain his grip on the handle of the trimming knife with sufficient pressure to prevent the handpiece from twisting or turning in his hand. This continuous pressure over extended periods of time, or throughout a usual work shift, fatigues the operator which decreases the amount of production or meat trimmed during a work shift. Also, the handles of the trimming knives, whether electrically operated or pneumatically operated, become coated with grease from the fat of the meat being trimmed, requiring sufficient pressure to be maintained on the handle to prevent the handle from turning in the operator's hand due to the rotational motion applied on the handle by the energy of the rotating blade.
Preferably an electric switch is not mounted on the handpiece itself for controlling the overhead electric motor due to the safety involved since the handpiece is usually used in a wet and damp environment and must be cleaned during and after each work shift for sanitary reasons. Therefore, it is impractical to have an electric control switch on the handpiece itself, which would permit an operator to conveniently stop and start the drive motor during momentary work stoppages throughout a work shift.
The pneumatic driven trimming knives have the disadvantage of requiring a control lever mounted on the handpiece which must be maintained in a depressed condition to maintain the air motor in an On condition. Such levers require the use of various sealing valves which, after periods of time, occasionally will leak causing a self-refrigeration effect due to the escaping of pressurized air around the sealing rings. This further increases the cooling or chilling of the operator's hand adding to the discomfort and fatigue. It has been found that operators will occasionally lock the control lever in a permanently ON position in order to eliminate maintaining the lever in the depressed position which results in an unsafe condition.
Futhermore, it is important that when actuating the power source for rotating the cutting blade of either the electrically or pneumatically operated handpieces that the operator have at least one hand on the handpiece with the other hand being at a sufficient distance from the blade to prevent accidental cutting upon starting the drive motor.
Another problem with prior art electric and pneumatic driven knives having a usually manually actuated ON/OFF switch is that the continuous running of the flexible drive shaft and pneumatic motor throughout much of the work shift increases the maintenance cost of the knife. This continuous operation requires more frequent replacement of the cutting blade, the blade housing, drive pinion gear, flexible drive cable and outer casing since the blade is rotating continuously even when the knife is not being actually used by the operator to trim the meat.
Therefore, the need exists for an improved ON/OFF control system for power operated hand tools, and in particular for power operated meat trimming knives, both electrically and pneumatically driven, which enables the knife to be stopped and started in a simple, economical, efficient, and particularly in a safe manner.